Air cushion sensor for tactile sensing during minimally invasive surgery

Abstract

A sensor is described for detecting the force applied to or by soft material, and that is thus able to measure the stiffness of a soft material. The sensor comprises a sensor body into which is supplied a fluid under pressure. At least one sensor members are provided that are arranged to project from the sensor body under the pressure exerted thereon by the fluid. A sensor member displacement detection system is also provided, that is preferably optically based using optical fibres to illuminate the sensor member and that measures the modulation of the light reflected from the sensor member as the member is displaced against the pressure of the fluid to detect and measure the displacement. From the measured displacement an estimate of the force being applied to the sensor member can be obtained. The sensor is of a small size suitable for use during MIS or catheterisation procedures. Preferably the sensor is constructed of non-metallic material such that it is MRI compatible.

Description

TECHNICAL FIELD[0001]The invention relates to a sensor for providing force feedback, and in particular although not exclusively during surgical procedures. More specifically, one embodiment of the invention relates to a sensor for measuring variations in the stiffness of soft tissue for use in, for example, minimally invasive surgery or catheterisation. Another embodiment relates to a sensor for sensing the force on vasculature or other body channel walls during catheterisation procedures.BACKGROUND TO THE INVENTION AND PRIOR ART[0002]Minimally Invasive Surgery[0003]Minimally invasive surgery (MIS) can be described as a form of surgery that is performed through a number of small incisions. The incisions vary in sizes ranging from 3-12 mm in diameter [3]. The incisions are strategically located so as to offer access to the surgical site. A camera is initially inserted through one of the incisions to obtain a field of view of the surgical site. Laparoscopic tools are then inserted thr...

AI Technical Summary

Benefits of technology

[0025]An object of the invention is to provide a sensor which is manoeuvrable and which can be used to give haptic feedback, i.e. tactile and / or force information. In one embodiment this allows the fast creation of mechanical images showing the stiffness and / or force distribution in a soft material and can be used, for example, to identify tissue abnormalities in soft tissue. In another embodiment it allows a catheter tip to be more accurately steered, and particularly by robotic systems, with less risk of tissue damage.

Problems solved by technology

However, MIS (also referred to as keyhole surgery) does have some major drawbacks according to [4].

First of all, the lack of direct access to the surgical site makes it impossible for surgeons to palpate and feel organs with their hands.

Another problem is that the friction between the laparoscopic tools and the trocar port and also the torque required to rotate the tools make it very difficult to sense the actually contact forces between the tool and tissue.

This fallback increases the possibility of accidental tissue trauma.

The third limitation is the loss of direct hand-eye coordination due to the fact that tools have to move around a fixed point reducing the degrees of freedom to four (excluding the tip's motion): pitch, yaw, roll and insertion [5].

None of the robotic systems are equipped with high quality feedback; this is of major concern as it can have potentially devastating consequences especially if the tools leave the field of view [5].

The drawback of this location is that it is far away from the surgical site and therefore the readings can be affected by friction, backlash, inertia and gravity.

The setback with placing the sensor in this location is that it can be affected by the friction and reaction forces from the insertion point.

The drawback with this location is that the space is very limited which generates the need for a very small sensing element.

The problem associated with the system proposed by [1], which employs a cylindrical wheel attached to a force / torque sensor, is that its manoeuvrability is limited to movements normal to the longitudinal axis of the used cylindrical wheel.

Nonetheless, this technique does come at a cost.

The ionising radiation (X-rays), which is emitted by a fluoroscope, generates a health risk for the patient and for the physician performing the examination.

This sets constraints to exposure time and the number of radiation doses emitted during the procedure.

Having said that, due to the use of ionising radiations (X-rays), physicians do not recommend theses scans without a good reason.

The uses of components that breach these rules cause either disturbance to the magnetic field and hence artefacts are produced in the resulting images, or make their operation completely useless.

Furthermore, the patient's health might be harmed from heating-up effects, or missile effects caused by non-MRI compatible materials which are exposed to the magnetic fields of the scanner.

Regardless of the haptic sense, physicians are incapable of identifying the origin of the forces.

These two forces are important in a catheterisation, but due to the complexity involved in distinguishing them, only surgeons with vast experience tend to perform them.

However, very few of them were developed for the detection of contact forces with the blood vessel walls.

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